Modern wind turbine designs seek to incorporate various blade monitoring systems, in order to provide for reliable and controlled operation of the wind turbine. Such monitoring systems can include blade deflection monitoring systems, which are used to provide an indication of wind turbine blade deflection or flexing during turbine operation. This information can be used to monitor for the risk of a future tower strike by the wind turbine blades, and to perform appropriate controller actions, e.g. blade pitching or turbine braking to minimize or eliminate such risk.
An example of such a deflection monitoring system is provided in U.S. Pat. No. 7,883,316, which describes a deflection monitoring system utilising a wireless communication network, operable to detect the position of various points along the length of the blade, and to determine blade bending from this information.
WO 2014 027032 suggests the use of external transceivers mounted at the root end of the wind turbine blade in communication with transceivers mounted at the tip end of the blade. Based on, for example, radio communication, measures the distance between the transceivers is measured. Positioning of the transceivers is optimized with respect to path loss between the devices.
US 2010/021298 discloses a wireless deflection monitoring system comprising a nacelle communication device.
WO 2009/143848 discloses an optical monitoring system.
However, it has been found that such wireless monitoring systems are vulnerable to various operational factors that may interfere with—and obscure the communication signal, for example, signal reflections, multipath effects, signal attenuation caused by passing through layers of different materials, etc., thereby reducing the precision and effectiveness of the monitoring system.
It is an object of the invention to provide an improved blade deflection monitoring system which is less susceptible to the above-described factors.